exmark not running right

I have a wb Exmark TT with the 17 hp kawasaki. For about a week now its been running poorly, sputtering off and on and just not running smooth. Ive changed plugs and the fuel filter with no success. Anyone with a guess of what else it could be?

Is it possible that it could be related to the safety feature on mowers that kills the engine when handle is released? Not sure what its called, but its a little small box with a button on the top located in the middle underneath the handlebars. Could that cause similar problems if something stopped functioning there?

If its not running smooth then its a carb issue. Take it apart, clean it, and rebuild it, or take it to someone who knows what there doing it let them do it. If a safety switch is bad then the machine wouldn't start/run.